1. Field of the Invention
The present invention relates to an ink detecting device useful for a printing apparatus such as a mimeograph apparatus and so forth, and more particularly to a motor-type ink sensor for detecting the presence or absence of ink by the driving condition of a motor which drives to rotate an agitating part in ink.
2. Description of the Related Art
As a means for detecting ink in a printing apparatus and so forth, an electrical capacitance ink detecting device as shown in FIG. 12 has been known. In this ink detecting device, an ink roller 100 and a squeegee roller 101, and an ink detecting electrode 103 which contacts an ink fountain defined therebetween serve as counter electrodes to constitute a capacitor. This capacitor and a coil not illustrated form an oscillatory circuit 104.
The oscillation frequency of the oscillatory circuit 104 is determined by the capacity of the capacitor when coil inductance is fixed. And the electrostatic capacity of the capacitor is determined by the quantity of ink. Therefore, the quantity of ink supplied between these rollers corresponds to the oscillation frequency of the oscillatory circuit 104, and the quantity of ink can be detected by use of this oscillation frequency.
According to the ink detecting device of electrostatic capacity type described above, it is imperative to accurately set the location of the detecting electrode 103 in relation to the rollers 100 and 101 in order to perform accurate ink detection. If the detecting electrode 103 is not accurately set, there will occur such a problem as inaccurate ink detection. Since there exists a limited space for mounting the detecting electrode within a narrow printing drum of the printing apparatus, the setting of the ink detecting device is much restricted.